Electronic musical instrument having dynamic range variable expression control

ABSTRACT

In an electronic musical instrument, an expression control circuit constituted by a first variable resistor is connected in the path of the tone signal. A second variable resistor is connected in series with or in parallel to the first. A third variable resistor is connected in shunt between the output side of the expression control circuit and the ground. The second and the third variable resistors can adjust the variation range of the tone signal at the output of the first variable resistance.

BACKGROUND OF THE INVENTION

1. Field of the invention:

This invention relates to an electronic musical instrument and moreparticularly to expression control means in an electronic musicalinstrument.

2. Description of the prior art:

Conventionally, expression control means have been used for controllingthe tone volume in electronic musical instruments. The expressioncontrol means is connected between the output of the tone coloringcircuit and the input of the amplifier and comprises a photoconductiveelement (variable resistance element) such as CdS element and a lightsource such as a lamp or a light emitting diode disposed opposite toeach other with a shutter plate disposed therebetween. The shutter platehas a through hole of a predetermined shape and is interlocked with afoot plate for the expression control so that the amount of lightimpinging on the photoconductive element continuously varies accordingto the depth of the foot plate depression. Thus, the resistance of thephotoconductive element is varied according to the depth of the footplate depression. Hence, the signal level derived from the tone coloringcircuit is controlled by the foot plate depression to effect theexpression control. The tone volume increases as the expression footplate is depressed.

According to the conventional expression control means, however, thedepression angle of the expression foot plate and the tone signal levelare related in one-to-one correspondence and the variationcharacteristic is constantly represented by a single curve and thevalues of the dynamic range and the minimum (or maximum) level are fixedand little, if at all varied.

Therefore, in an ensemble play, etc., it is very difficult to carry outthe optimum tone volume control. Namely, when one wishes to play theinstrument in a narrow tone volume range he should produce expression byminute variations of the foot plate depression, whereas to play theinstrument in a wide tone volume range he should manipulate the footplate almost from the minimum position to the maximum position. Hence,well-trained skill is required for the manipulation of the foot plate.

Further, in such an electronic musical instrument having a plurality oftone generating systems, e.g. one for strings, one for flute, etc., whenthe plurality of tone generating systems is operated simultaneously toprovide musical sounds of a plurality of instruments, the tone volumecontrol by the manipulation of an expression foot plate becomes commonfor the respective tone generating systems. Hence, musical play rich inmusicality cannot be achieved.

In other words, although an electronic musical instrument has anadvantage that one can perform a musical play resembling an ensembleplay by a plurality of players, it cannot give variations of musicaltones nor accents due to the differences in the dynamic ranges of thetone volumes of the respective musical instruments. Usually, the dynamicrange of the tone volume is largest for the melody instrument. Inconventional electronic musical instrument, however, performance effectdue to the variations in the dynamic range has not been provided.

Further, it has been also proposed to dispose a plurality ofphotoconducting elements against a light source with shutter plates ofpredetermined shape intervening therebetween. However, the number ofshutter plates interlocked with an expression foot plate is at most two.Thus, to afford expression control for more than two tone generatingsystems is practically impossible according to this method. It can bethought of to provide an expression foot plate for each tone generatingsystem. This leads to very complicated manipulation and musicalperformance rich in variety cannot be easily achieved.

To solve the above problem, it has been recently proposed to dispose theends of a plurality of optical fibers against a light source through ashutter plate and a plurality of photoconducting elements at the otherends of the optical fibers. These photoconducting elements are connectedin the circuits for controlling the signal levels in the respective tonesignal generating systems. Thus, the tone volume control for a pluralityof tone signal generating systems can be achieved by the manipulation ofa single expression foot plate. Such a system can achieve the tonevolume control of a plurality of tone signal generating systems by asingle expression foot plate, but because of the use of optical fibersit is accompanied by the practical inconveniences, such as troublesomemanufacture, larger size or higher cost.

SUMMARY OF THE INVENTION

This invention intends to solve the drawbacks and inconveniences asdescribed above.

An object of this invention is, therefore, to provide expression controlmeans in an electronic musical instrument capable of arbitrarily varyingat least either the dynamic range or the minimum level of the tonesignal and preferably both.

Another object of this invention is to provide expression control meansin an electronic musical instrument capable of varying the dynamic rangeand the minimum level for the tone signal in an interlocked manner.

A further object of this invention is to provide expression controlmeans for a plurality of tone signal generating systems in an electronicmusical instrument capable of easily and differently controlling thetone signal levels in the respective tone signal generating circuits.

Yet a further object of this invention is to provide an electronicmusical instrument having an expression control having a plurality oftone signal generating systems and expression control means capable ofcontrolling the tone volume of the respective tone signal generatingsystems, the dynamic range and the minimum level of the tone volumebeing arbitrarily variable at least for one tone signal generatingsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of an electronic musicalinstrument according to this invention.

FIG. 2A is a schematic electric circuit diagram of an embodiment ofexpression control means to be embodied in the electronic musicalinstrument of FIG. 1 according to this invention, and FIGS. 2B and 2Care characteristic charts of the expression control means of FIG. 2A.

FIG. 3A is a schematic electric circuit diagram of another embodiment ofexpression control means to be embodied in the electronic musicalinstrument of FIG. 1 according to this invention, and FIGS. 3B and 3Care characteristic charts of the expression control means of FIG. 3A.

FIG. 4 is a schematic electric circuit diagram of a further embodimentof expression control means according to this invention.

FIG. 5A is an electric circuit diagram of a concrete embodiment ofexpression control means according to this invention, and FIG. 5B is achart of characteristic curves of the circuit of FIG. 5A.

FIGS. 6 and 7 are schematic block diagrams of electronic musicalinstruments according to embodiments of this invention.

FIG. 8 is a block diagram of an electronic musical instrument accordingto an embodiment of this invention.

FIGS. 9 and 10 are schematic electric circuit diagrams of expressioncontrol means to be used in the electronic musical instrument of FIG. 8according to this invention.

FIG. 11 is a schematic electric circuit diagrams of another embodimentof expression control means according to this invention.

FIGS. 12 and 13 are schematic circuit diagrams of examples of theattenuator circuit to be used in the circuit of FIG. 11 according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an electronic musical instrument, in which tone signalsgenerated in tone generators 10 are supplied through tone keyers 11, 12and 13 and tone coloring filters 18, 19 and 20 to expression controlmeans 21, 22 and 23. The tone keyers 11, 12 and 13 are actuated by anupper keyboard 15, a lower keyboard 16 and a pedal keyboard 17,respectively. A latching selector 14 is provided to the pedal keyboard17. Thus the tone signal generating system for the pedal keyboard isprovided with only one tone keyer 13. The tone coloring filters 18, 19and 20 color the tone, e.g. flute, clarinet, etc. and supply outputs tothe expression control means 21, 22 and 23 which are interlocked with asingle foot plate 24. The expression control means 21, 22 and 23 areprovided with respective controlling manipulators 25, 26 and 27 so as tovary the minimum level and the dynamic range for the tone volume andsupply outputs to a loudspeaker system 29 through an amplifier 28.

When a key in the upper keyboard 16 is depressed, a corresponding tonekeyer is driven open and a corresponding tone signal generated in thetone generators 10 is fed to the tone coloring filter 18. The filter 18colors a musical tone signal and supplys it to the expression control21. The dynamic range and the minimum level for the tone of the upperkeyboard developed by depression of foot plate 24 can be controlled byadjusting the manipulator 25. The tone signal is attenuated in theexpression control means 21 according to the set position of themanipulator 25 and the depression angle of the expression foot plate 24to supply a controlled tone signal to the loudspeaker system 29 throughthe amplifier 28.

In FIG. 2A, photoconductive element 31 is disposed against a lightsource 32 through a shutter plate 33 having a through hole of apredetermined shape. A variable resistor VR1 is connected between thephotoconductive element 31 and the amplifier 28 and another variableresistor VR2 is connected between the input terminals of the amplifiers28. In FIG. 2A, controls corresponding to controls 22 and 23 of FIG. 1are omitted for clarity. These controls contain similar resistorssimilarly connected. These resistors form a voltage-dividing circuit.Typical values for these resistances are as follows: the photoconductingelement 31 is from 1MΩ (dark) to 1KΩ, VR1 is from 200KΩ to 1KΩ, and VR2is from 40KΩ to 2KΩ. The shutter plate 33 is interlocked with the commonexpression foot plate 24. When the expression foot plate 24 isdepressed, the shutter plate 33 is displaced correspondingly and theamount of light impinging from the light source 32 onto thephotoconducting element 31 is varied. Hence, the resistance of thephotoconducting element 31 changes accordingly and the signal levelsupplied from the tone coloring filter 18 to the amplifier 28 is variedaccording to the resistance of the photoconducting element 31. Thus,when the expression foot plate 24 is depressed, the amount of light(intensity) impinging on photoconducting element 31 increases and theresistance of photoconducting element 31 decreases. Hence, the ratio ofthe voltage established across the variable resistor VR2, i.e., theinput signal level for the amplifier, to the output voltage of the tonecoloring filter 18 increases to produce louder sound. The variableresistors VR1 and VR2 are interlocked with the manipulator 25 which isdisposed on a manipulation panel (not shown).

To help understanding of the circuit of FIG. 2A, the cases when each oneof variable resistances VR1 and VR2 is changed will be considered first,referring to FIG. 2B. In FIG. 2B, the abscissa represents the depressionof the expression foot plate 24 and the ordinate represents the signallevel at the input of the amplifier 28 represented in dB. Solid line arepresents the standard state where the variable resistances VR1 and VR2take medium values. When the foot plate 24 is released, thephotoconductive element 31 receives little light and has a largeresistance, e.g. 1MΩ. As the foot plate 24 is depressed, the resistanceof the photoconductive element 31 decreases and the signal levelestablished across the variable resistor VR2 increases. The resistanceof the variable resistor VR1 plays almost no role at the releasedposition since the dark resistance of the photoconducting element 31 isvery large, but an important role for determining the gradient of thecharacteristic curve as the foot plate 24 is depressed. On the otherhand, the resistance of the variable reistor VR2 plays a main role fordetermining the voltage dividing ratio and hence the signal levelthroughout the foot plate depression range, but a relatively small rolein determining the gradient of the characteristic curve.

When the variable reistance VR1 is decreased, the characteristic curveis changed, for example, to dotted line b. On the other hand, if thevariable resistance VR1 is increased, the characteristic curve ischanged, for example, to dotted line c.

As is apparent from the above, the dynamic range of the tone volume canbe effectively varied by the variable resistance VR1. Here, the minimumlevel is hardly changed by variation of the resistance VR1.

When the resistance VR2 is varied, the minimum level is effectivelyvaried. Namely, when the resistance VR2 is increased, the minimum levelincreases to generate a characteristic curve as shown by broken line d.When the resistance VR2 is decreased, the minimum level decreases togenerate a characterstic as shown by broken line e. Here, the dynamicrange is subjected to small change by the variation of the resistanceVR2 since the resistance VR2 is small compared to the resistance of thephotoconductive element 31 and/or the resistance VR1.

When the variable resistances VR1 and VR2 are interlocked to vary in thesame direction, the characteristic curve changes as are shown by dottedlines in FIG. 2C. In FIG. 2C, solid line a represents the standardstate. If the resistances VR1 and VR2 are decreased, the characteristiccurve becomes as shown by dotted line f (c.f. lines b and e in FIG. 2B).If the resistances VR1 and VR2 are increased, the characteristic curvebecomes as shown by dotted line g (c.f. lines c and d in FIG. 2B).

On the other hand, if the variable resistances VR1 and VR2 are varied inopposite directions, the characteristic curve changes as shown by brokenlines in FIG. 2C. Namely, when the resistance VR1 is decreased and theresistance VR2 is increased, the characteristic curve becomes as shownby broken line h. When the resistance VR1 is increased and theresistance VR2 is decreased, a characteristic curve as shown by brokenline i is produced.

Thus, the dynamic range and the minimum level can be varied byinterlocking the variable resistors VR1 and VR2 and varying theresistances thereof.

FIG. 3A shows another example of the expression control means, in whicha variable resistance VR3 is connected parallel to the photoconductingelement 31 and another variable resistance VR4 is connected between theinput terminals of the amplifier 28. The parallel connection of theresistances of the photoconducting element 31 and the variableresistance VR3 forms a first resistive portion and the resistance VR4forms a second resistive portion. The series connection of the first andthe second resistive portions forms a voltage dividing circuit and theoutput voltage is established across the second resistive portion,similar to the case of FIG. 2A. In this case, however, the resistanceVR3 performs an opposite function to that of VR1 of FIG. 2A.

Similar to the case of FIG. 2A, the respective influences of theresistances VR3 and VR4 will be described first. When the resistance VR4is fixed and only the resistance VR3 is varied, the characteristic curvevaries from one represented by solid line a' to those represented bydotted lines b' and c'. Namely, when the resistance VR3 is increased(decreased), the resistance of the first resistive portion is increased(decreased) unless the photoconductive element is almost conductive.Thus, the signal level established across the resistance VR4 decreases(increases) and the characteristic curve changes from one as representedby solid line a' to one as represented by dotted line b' (c'). Here, themaximum level is subjected to small change since the resistance of themaximumly illuminated photoconducting element is very small compared tothe resistance VR3. When only the resistance VR4 is varied, the voltagedividing ratio is changed. Namely, when the resistance VR4 is increased(decreased), the signal level established thereacross also increases(decreases) and the characteristic curve as represented by solid line a'varies to one as represented by dotted line d' (e'). In short, thedynamic range can be effectively varied by the variable resistance VR3and the maximum level by the variable resistance VR4.

When the variable resistances VR3 and VR4 are interlocked and varied inthe same direction, the characteristic curve represented by a' varies tothose as represented by f' (larger VR3 and VR4) and g' (smaller VR3 andVR4). On the other hand, when they are varied in opposite direction, thecharacteristic curve varies to those as represented by h' (smaller VR3and larger VR4) and i' (larger VR3 and smaller VR4).

As is apparent from the above description, the dynamic range and themaximum or minimum level can be effectively varied by adjusting variableresistors connected to an expression controlling variable resistor(photoconducting element).

FIG. 4 shows a further embodiment for varying the dynamic range and theminimum level, which may be considered equivalent to the circuit of FIG.2A. A variable resistance VR1 is connected in series to thephotoconducting element 31 so as to vary the dynamic range, but in thisembodiment a variable resistor VR6 is connected across the amplifier 28so as to vary the amplification factor of the amplifier 28 and hence tovary the dynamic range. Another variable resistor VR5 is connectedbetween the input terminals of the amplifier 28 which works to vary theminimum level.

FIG. 5A shows a concrete embodiment of the circuit for changing thedynamic range and the minimum level of the tone signal based on theequivalent circuit of FIG. 2A. In the figure, a photoconducting element31 disposed against a light source 32 through a shutter plate 33 formsan expression controlling element and is connected in parallel with aresistor R1 and with an amplifier 28 through a resistive network. Aphotocoupler consisting of a photoconducting element 35 and a lightemitting diode 36 works as a variable resistor VR10. The resistivenetwork including resistors R2 and R3 and the variable resistors VR7 andVR10 couples the photoconducting element 31 and the amplifier 28. Amanipulator 37 corresponding to those 25, 26 and 27 consists of avariable resistor and is disposed on a manipulation panel (not shown).The movable terminal of the variable resistor 37 is connected to thebase of a transistor Tr1. The base bias is given by a voltage dividingnetwork consisting of resistors R7, R8 and R9 and the variable resistor37. Resistors R6 and R10 work as a collector resistor and an emitterresistor. Series connection of a resistor respectively R4 and acapacitor C1 works to give loudness control effect. A variableresistance VR8 is connected between the output and the input of theamplifier 28 to control the amplification factor, and R5 is a resistor.

When the manipulator 37 is manipulated, the base bias for the transistorTr1 is varied and the collector current is varied. Since the lightemitting diode 36 is connected with the collector of the transistor Tr1,the amount of the light emitted from the light emitting diode 36 isvaried according to the collector current and the impedance of thephotoconducting element 35 is varied correspondingly. When theresistance of the photoconducting element 35 becomes smaller, a largercurrent is by-passed through the resistors 35 and R4 and the capacitorC1. When the resistance of the element 35 becomes larger, a largercurrent is made to flow through the resistor R2. The parallel connectionof the two resistances 35 and R3, the resistance R2 and the resistanceVR7 constitute a three terminal network of a delta shape which can beconsidered to be equivalent to a three terminal network of a Y shapeconsisting of three branch resistances. Therefore, the single variableresistor VR10 constituted by the photoconducting element 35 works therole of the two variable resistors VR1 and VR2 of the circuit of FIG.2A. The dynamic range and the minimum level are varied according to theamount of light impinging on the element 35. The variable resistor VR7can also be adjusted to control the circuit characteristics.

In a concrete example, resistor R1 was 1MΩ, R2 270KΩ, R3 1MΩ, R4 1KΩ, R510KΩ, R6 560Ω, R7 6.8KΩ, R8 5.6KΩ, R9 10KΩ, R10 47Ω, resistances 31 and35 1MΩ to 1KΩ, VR7 B class 100KΩ maximum, VR8 B class 500KΩ maximum,resistance 37 A class 10KΩ maximum, and C1 180 nF. The characterisitccurves in this case are shown in FIG. 5B. In FIG. 5B, curve k representsthe characteristic when the movable contact of the variable resistor 37is at a medium position, curve l the characteristic when the movablecontact is at the highest position, and the curve m the characteristicwhen the movable contact is at the lowest position. As can be seen fromthe figure, the dynamic range is -27 to -4 dB for the curve k, -22 to-4.5 dB for the curve l and -42 to 0 dB for the curve m.

FIG. 6 shows an electronic musical instrument in which a plurality oftone signal generating systems is operated by a single keyboard. Namely,a keyboard 15 triggers both of tone keyers 41 and 42. The tone signalsgenerated in the tone generators 10 and allowed to pass through the tonekeyers 41 and 42 are supplied to an amplifier 28 through respective tonecoloring filters 43 and 44 and expression control circuits 45 and 46provided with manipulators 47 and 48 for varying the dynamic range. Theexpression control circuits may be of any structure describedhereinabove or hereinbelow.

FIG. 7 shows another embodiment of an electronic musical instrument inwhich two tone signal generating systems are provided and actuation ofthe two may be coupled. Namely, an upper and a lower keyboards 15 and 16provided to actuate tone keyers 41 and 42 may be coupled by a couplingswitch Cs. Further, tone volume controlling variable resistors VR11 andVR12 are connected between the tone coloring circuits 43 and 44 and theexpression control means 45 and 46, and a balancing variable resistorVR9 is provided at the input of the amplifier 28. The expression controlcircuits 45 and 46 are similar to those of FIG. 6 and are interlockedwith an expression foot plate. Manipulators 47 and 48 may vary thedynamic range of the respective tone signals similar to those of FIG. 6.Means for varying the dynamic range may not be provided to all of thetone signal generating systems.

In the foregoing embodiments, the dynamic range is arranged to becontinuously variable by means of variable resistors, but precisecontrol of a manipulator through continuous adjustment requires care.Thus, in the course of performance rapid and precise control of amanipulator is difficult through continuous manner. Especially whenthere are multiple tone signal generating systems, rapid and precisecontrol of the respective dynamic range through continuous manner isvery difficult. The embodiment of FIG. 8 is to eliminate this drawback.

FIG. 8 shows an electronic musical instrument comprising tone generators10, tone keyers 11, 12 and 13, upper, lower and pedal keyboards 15, 16and 17, tone coloring circuits 18, 19 and 20, a rhythm device 49,expression control means 21, 22, 23 and 50, switching means 51, 52, 53and 54, an expression foot plate 24, an amplifier 28, and a loudspeakersystem 29. The expression foot plate 24 is interlocked with theexpression control means 21, 22, 23 and 50 the dynamic ranges of whichare controllable by on-off or multi-position switches 51 to 54 disposedon a manipulation panel (not shown) or at any convenient positions.

The expression circuit 21, 22, 23 and 50 may have a similar structure asshown in FIGS. 9 and 10. In FIG. 9, a photoconducting element 31 forminga part of an expression control circuit is connected between a tonecoloring circuit 18 and the amplifier 28. Shunt resistors R14 and R15are connected in parallel with the photoconducting element 31 throughswitches S1 and S2. The number of these shunt resistor circuits can beselected arbitrarily. A compensation network comprising resistors R11,R12 and R13 and a capacitor C2 is also connected across thephotoconducting element 31 for a loudness control. Between the input andoutput terminals of the amplifier 28, a resistor R 16 and seriesconnections of resistors R17 and R18 and switches S3 and S4 areconnected in parallel. The switches S1-S3 and S2-S4 are interlocked andactuated by a switching circuit 55 which is activated by themanipulation switch 51. The switchng circuit 55 may comprise a flip-flopcircuit or a relay circuit. Whenthe expression foot plate 24 (FIG. 8) isdepressed, a shutter plate having a predetermined through hole isdisplaced and the amount of light impinging on the photoconductingelement 31 is varied to vary the signal level supplied to the input ofthe amplifier 28. If the switches S1 and S3 are closed, the range of theinput signal level for the amplifier 28 becomes high and narrow. Thus,the dynamic range is varied. The resistor R17 connected between theinput and output termnals of the amplifier 28 decreases theamplification factor and hence works to compensate the effect of theresistor R14. As the result, the resistor R17 varies the average signallevel supplied to the loudspeaker system 29. Since the switches S1 andS3 (and S2 and S4) are interlocked, the dynamic range can be varied byactuating the switch S1 (and S2) and the change in the average signallevel accompanied with the change in the dynamic range can becompensated for by actuating the switch S3 (and S4).

FIG. 10 shows another embodiment of the expression control means, inwhich the photoconducting element 31 is connected between the outputterminals of the tone coloring circuit through a resistor. Namely, theoutput voltage of the tone coloring circuit is divided by a seriesresistance of the resistors and the voltage established across thephotoconducting element is supplied to the input terminals of theamplifier 28 through a resistive network. A series connection of aresistor R19 and a switch S5 is connected in parallel with thephotoconducting element 31 to reduce the effect of the variation in theresistance 31. Resistors R20 and R21 and a switch S6 are connectedbetween the input and the output terminals as shown in the figure. Theswitches S5 and S6 are interlocked and actuated by switching means 55similar to the case of FIG. 9.

When the switch 51 is manipulated, the resistance R19 is connected inparallel with the photoconducting element 31 to vary the dynamic rangeof the colored tone signal and the switch S6 connects the resistor R21between the input and the output terminals of the amplifier 28 to changethe amplification factor of the amplifier 28 and thus to compensate forthe change in the average signal level accompanying with the change inthe dynamic range.

It will be apparent that switches 51 to 54 may be operated commonly orseparately. Further, the resistors R4, R5, R9, etc. may be replaced withvariable resistors so as to vary the dynamic range continuously.

When the number of tone signal generating systems is not small andmechanical interlocking system in the expression control systems bringsproblem, an interlocking system as shown in FIG. 11 may be adopted forthe multi-channel embodiments. The circuit of FIG. 11 shows only how aplurality of expression control circuits are driven by a single footplate. The portions for varying the dynamic range are not shown, but itwill be apparent that such portions can be easily incorporated.

In FIG. 11, a block 21' including a light source 32, a photoconductingelement 31 and a shutter plate 33 interlocked with an expression footplate 24 forms a usual portion of an expression control circuit. Theoutput of the expression control circuit portion 21' is supplied to thebase of a transistor Tr2 to control the collector current thereof. Thecollector current flows through a light emitting diode D1 and controlsthe light impinging on a photoconducting element 56. Variations in theresistance of the photoconducting element 56 appear as variations of thecurrent flowing through the photoconducting element 56 and lightemitting diodes D2, D3 and D4. Namely, a block 55 forms avoltage-current converter and a block 57 forms a photo-coupler.Photo-couplers 59, 62 and 65 are formed with the light emitting diodesD2, D3 and D4, respectively. Photoconducting elements 58, 61 and 64constitute parts of the photo-couplers 59, 62 and 65 and also componentsof attenuating circuits 60, 63 and 66 which reduce the signal levelssupplied from terminals T1 to Tn at a desired ratio determined by theexpression foot plate 24. Namely, when the expression foot plate 24 isdepressed, the attenuating ratios of the attenuator circuits 60, 63 and66 are reduced.

The attenuator circuits 60, 63 and 66 may have a similar structure asshown in FIGS. 12 and 13. FIG. 12 shows a simplest form of theattenuator circuit which simply comprises a photoconducting element.FIG. 13 shows another form of the attenuator circuit which comprises aphotoconducting element and a loudness control circuit.

We claim:
 1. An electronic musical instrument comprising means definingat least one tone signal path for passing a tone signal therethrough,said path including an output terminal and an expression controlcircuitry, said circuitry having a first variable impedance element forselectively varying the level of the tone signal passing through saidpath and a variable impedance network, said variable impedance networkbeing connected to said first variable impedance element for adjusting,independently of the variation of said level, the variation range of thetone signal at said output terminal.
 2. An instrument according to claim1, wherein the number of said signal paths is at least two, each signalpath including expression control circuitry having a first variableimpedance element for varying the level of the tone signal passingthrough said path, and wherein said first variable impedance elements inthe respective paths are interlocked.
 3. An instrument according toclaim 2, wherein each of said first variable impedance elements consistsof a photo-coupler including a light emitting element and aphotoconducting element, said light emitting elements being connected inseries to be energized by a same current which is variable.
 4. Aninstrument as in claim 1 wherein said instrument includes an amplifierhaving first and second input terminals and wherein said networkincludes a first variable resistor serially connected between saidelement and one of said amplifier input terminals and a second variableresistor connected between said input terminals of said amplifier.
 5. Aninstrument as in claim 4 wherein said instrument further includescontrol means connected to said first and second resistors for varyingthe resistance thereof.
 6. An instrument as in claim 4 wherein saidelement is a photoresistive element.
 7. An instrument as in claim 1wherein said instrument includes an amplifier having first and secondinput terminals and wherein said network includes a first variableresistor connected in parallel with said element and a second variableresistor connected between said input terminals of said amplifier.
 8. Aninstrument as in claim 1 wherein said instrument includes an amplifierhaving first and second input terminals and an output terminal andwherein said network includes a first variable resistor connectedbetween one of said amplifier input terminals and said amplifier outputterminal and a second variable resistor connected between said inputterminals of said amplifier.
 9. In an electronic musical instrument ofthe type having means for generating at least one tone signal, means foramplifying said tone signal, expression control means connected betweensaid generating means and said amplifying means for controlling the tonevolume, and manually operated means for varying said volume, theimprovement wherein said control means includes first and secondvariable resistor means connected to said varying means for resistancevariation independently of said varying means, first circuit means forconnecting said first resistor means so that variation thereof variesthe range of the signal applied to said amplifying means and secondcircuit means for connecting said second resistor means so thatvariation thereof varies an extreme level of said range.
 10. In aninstrument as in claim 9 wherein said amplifying means includes firstand second terminals and said control means further includesphotoresponsive means, a light source and a manually operable shutterplate between said source and the photosensitive means.
 11. In aninstrument as in claim 10 wherein said first circuit means connects saidfirst resistor means serially between said photoresponsive means and oneof said terminals and said second circuit means connects said secondresistor means between said first and second terminals to vary theminimum level of said range.
 12. In an instrument as in claim 10 whereinsaid first circuit means connects said first resistor means in parallelwith said photoresistive means and said second circuit means isconnected between said first and second terminals to vary the maximumlevel of said range.
 13. In an instrument as in claim 9 furtherincluding means for varying simultaneously the resistance of said firstand second resistor means.